Plastic articles have found a variety of use. For example, plastic optical articles (such as video discs and ophthalmic lenses) are widely used in place of such articles made from ground glass because the former are light in weight and inexpensive to produce. As disclosed in U.S. Pat. Nos. 3,380,460 and 3,931,373, the most widely used plastic ophthalmic lens material is polymerized diethylene-glycol bis(allyl carbonate). This polymer is characterized by excellent clarity, resistance to discoloration, high strength, and high impact resistance. However, polymerization of diethyleneglycol bis(allyl carbonate) is generally accompanied by high shrinkage during cure (e.g., from 11 to 14%) and extended curing time (e.g., from 5 to 16 hours or more). The high shrinkage levels create difficulties in the production of plastic ophthalmic lenses from this material, particularly in the production of lenses having large differences in thickness between the center and edges of the lens. The extended cure times tie up production facilities and lead to inefficient utilization of the dies in which the lenses are molded. Also, the thermal cure cycle used to polymerize the monomer consumes large amounts of energy and undesirably thermally stresses the glass dies. Furthermore, the abrasion resistance of ophthalmic lenses made from this monomer is not satisfactory. Consequently, such lenses are typically coated to improve their abrasion resistance. The application of such coatings introduces problems such as adhesion failure, crazing, index of refraction differences, and flow lines. This last problem is particularly troublesome with multifocal lenses.
Some polymerizable compositions containing four or more ethylenically-unsaturated carbamic ester groups and a copolymerizable diluent monomer have been broadly included in proper disclosures. See, for example, U.S. Pat. Nos. 3,509,234; 3,700,643; 3,782,961; 3,907,865; 3,928,299; 3,954,584; 3,954,714; 4,006,024; 4,072,770; 4,108,840; 4,112,017; 4,131,602; 4,133,723; 4,188,455; 4,228,232; 4,246,391; 4,287,323; and 4,330,657; and U.K. Published Patent Application No. 2,050,396 A.
These disclosures are related to thin-film or coating compositions such as paints, varnishes, printing plates and photoresists, which are generally less than two millimeters thick. They fail to describe which, if any, of those compositions would have a desired balance of useful properties such as low polymerization shrinkage, low viscosity, absence of coloration, high hardness, resistance to stress cracking, and an abrasion resistance of greater than 140 kilopascals (kPa) (20 psi). Additionally, they fail to teach how to obtain resins providing the desired balance of properties which are useful for providing cast articles such as plastic ophthalmic lenses and which eliminate the need for coating the articles with an abrasion resistant coating. Moreover, many of the compositions shown in these references are derived from diisocyanates (e.g., toluene diisocyanate), and the resulting compositions have two or more urethane linkages in each side chain. These compositions generally have too high a viscosity to be useful for optical casting purposes.
Compositions which contain four or more ethylenically-unsaturated carbamic ester groups attached to a polyester, polyether, or polyacrylate backbone and articles prepared therefrom have been disclosed in EPO No. 0068632, published May 1, 1983. The resins disclosed therein can be diluted with up to 50% by weight of one or more diluent monomers having one or more ethylenically-unsaturated groups and can be cured in castings having a thickness greater than about 2 millimeters to form articles having Barcol hardness of greater than about 15. However, these compositions do not have an abrasion resistance greater than about 700 kPa (about 100 psi).